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When a function is inlined, it can expose other functions as candidates for specialisation, but GHC doesn't specialise them.

For instance, given the two modules

module A where

{-# INLINABLE fac #-}
fac :: Num a => a -> a
fac 0 = 1
fac n = n * fac (n-1)

{-# INLINE f #-}
f :: Num a => a -> a
f a = fac a

module B where

import A

g :: Int -> Int
g x = f x

we see that f is inlined, but fac isn't specialised for Ints:

B.g :: Int -> Int
[GblId,
 Arity=1,

 Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=1, Value=True,
         ConLike=True, Cheap=True, Expandable=True,
         Guidance=IF_ARGS [0] 30 0}]
B.g =
  \ (x_ary :: Int) ->
    A.fac @ Int $fNumInt x_ary

Removing the INLINE pragma on f doesn't help.

Either of the following changes will cause fac to be specialised:

• adding # SPECIALISE f :: Int -> Int # to module B
• defining "g x = fac x" instead

This happens with both GHC 7.0.3 and GHC HEAD

Trac metadata

Trac field	Value
Version	7.0.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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